Heat-sensitive recording material

ABSTRACT

Disclosed herein is a heat-sensitive recording material in which a chromogenic dye-procursor comprises: 
     (A) a mixture comprising at least two divinyl phthalide compounds represented by the formula (I): ##STR1## wherein R 1  and R 2  represent respectively alkyl group of 1 to 6 carbon atoms, alkyl group of 1 to 4 carbon atoms having an alkoxy group of 1 to 4 carbon atoms or cycloalkyl group of 5 to 7 carbon atoms, X 1  and X 2  represent respectively hydrogen atom, alkyl group of 1 to 8 carbon atoms, alkoxy group of 1 to 8 carbon atoms, alkoxy group of 1 to 4 carbon atoms having an alkoxy group of 1 to 4 carbon atoms, cycloalkoxy group of 5 to 7 carbon atoms, alkenyloxy group of 3 to 8 carbon atoms, benzyloxy group, substituted benzyloxy group, furfurloxy group, tetrahydrofurfuryloxy group, phenyl group, substituted phenyl group, phenoxy group, substituted phenoxy group, fluorine atom, chlorine atom or bromine atom, m and n represent 0 or integer of 1 to 4, m+n=4 and R 1  and R 2  may join together to form a heterocyclic ring, or 
     (B) a mixture of the divinyl phthalide compound(s) represented by the formula (I) and at least one compound selected from the compounds represented by the formulas (II), (III) and (IV): ##STR2## wherein R 3  -R 14  represent alkyl group of 1 to 6 carbon atoms, alkyl group of 1 to 4 carbon atoms each having an alkoxy group of 1 to 4 carbon atoms, cycloalkyl group of 5 to 7 carbon atoms, phenyl group, substituted phenyl group or tetrahydrofurfuryl group, p and q represent 0 or integer of 1 to 4 p+q=4, X 3  represents hydrogen atom, alkyl group of 1 to 4 carbons or chlorine atom, X 4  and X 5  respectively represent hydrogen atom, alkyl group of 1 to 4 carbon atoms, flurine atom, chlorine atom or trifluoromethyl group, R 3  and R 4 , R 5  and R 6 , R 7  and R 8 , R 9  and R 10 , R 11  and R 12 , and R 13  and R 14  may join together to form heterocyclic rings.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is a continuation-in-part of application Ser.No. 037,669, filed Apr. 13, 1987 and application Ser. No. 037,665, filedApr. 13, 1987.

BACKGROUND OF THE INVENTION

The present invention relates to a heat-sensitive recording materialwherein a developed black color image shows absorption in the nearinfrared region and is excellent in moisture resistance, resistance toplasticizer, oil resistance and light fastness. More specifically, thepresent invention relates to a heat-sensitive recording materialcomprising, as a chromogenic dye-precursor,

(A) a mixture comprising at least two divinyl phthalide compoundsrepresented by the formula (I): ##STR3## wherein R¹, R² representrespectively alkyl group of 1 to 6 carbon atoms, alkyl group of 1 to 4carbon atoms having alkoxy group of 1 to 4 carbon atoms or cycloalkylgroup of 5 to 7 carbon atoms, X¹, X² represent respectively hydrogenatom, alkyl group of 1 to 8 carbon atoms, alkoxy group of 1 to 8 carbonatoms, alkoxy group of 1 to 4 carbon atoms having alkoxy group of 1 to 4carbon atoms, cycloalkoxy group of 5 to 7 carbon atoms, alkenyloxy groupof 3 to 8 carbon atoms, benzyloxy group, substituted benzyloxy group,furfuryloxy group, tetrahydrofurfuryloxy group, phenyl group,substituted phenyl group, phenoxy group, substituted phenoxy group,fluorine atom, chlorine atom or bromine atom, and m and n represent 0 orinteger of 1 to 4, n+m=4 and R¹ and R² may join together to form aheterocyclic ring, or

(B) a mixture of the divinyl phathalide compound(s) represented by theformula (I) and at least one compound selected from the compoundsrepresented by the formulas (II), (III) and (IV). ##STR4## wherein R³-R¹⁴ represent alkyl group of 1 to 6 carbon atoms, alkyl group of 1 to 4carbon atoms having alkoxy group of 1 to 4 carbon atoms, cycloalkylgroup of 5 to 7 carbon atoms, phenyl group, substituted phenyl group ortetrahydrofurfuryl group, p and q represent 0 or integer of 1 to 4,p+q=4 and X³ represents hydrogen atom, alkyl group of 1 to 4 carbonatoms or chlorine atom, X⁴, X⁵ represent hydrogen atom, alkyl group of 1to 4 carbon atoms, chlorine atoms, fluorine atom or trifluoromethylgroup, and each of R³ and R⁴, R⁵ and R⁶, R⁷ and R⁸, R⁹ and R¹⁰, R¹¹ andR¹², and R¹³ and R¹⁴ may join together to form a heterocyclic ring.

Heat-sensitive recording paper sheets using so-called leuco dyes havegenerally been used as recording paper for facsimiles and variousprinters, POS (point of sales) labels, railway tickets, etc. and thedemands for the same have increased rapidly, since they have theappearance of ordinary paper, require no fixing because of primary colordevelopment and enable high speed recording with no noises, and thedevices using them are small in the size, reduced in the weight,inexpensive and are free from maintainance work.

It is important for such heat-sensitive recording paper sheet that it isfree from background coloration and excellent in color developmentsensitivity, color development density, and light fastness and storagestability (moisture resistance, resistance to plasticizer, oilresistance, etc.) of developed color image. It is also important that aheat-sensitive recording paper wherein developed color image showsabsorption at the near infrared region has the same properties as above,but no satisfactory material has yet been obtained at present.

For improving the light fastness and the storage stability of thedeveloped color image, it has been known to use of a mixture of two ormore of chromogenic dye-precursors as described, for example, inJapanese Patent Publication No. 59-53193 (1984) (U.S. Pat. No. 4226912),Japanese patent application laying-open (KOKAI) Nos. 56-105990 (1981),57-123085 (1982), 58-71192 (1983), 58-119892 (1983) and 61-76387 (1986).However, any mixture disclosed in these publications is prepared bymixing fluoran compounds with each other and thus it cannot always besaid that the light fastness and the storage stability of developedcolor images are excellent.

The present inventors have made an earnest study for improving theforegoing drawbacks and, as a result, it have been found that thestorage stability of the developed color image can be improved and thecolor developing sensitivity and the light fastness of the image canalso be improved unexpectedly when a mixture prepared by mixing at leasttwo divinyl phthalide compounds of the formula (I) or mixing the divinylphthalide compound(s) of the formula (I) with at least one compoundselected from the compounds represented by the formulas (II), (III) and(IV) is used as a chromogenic dye-precursor, and based on this findings,the present invention has been accomplished.

SUMMARY OF THE INVENTION

In an aspect of the present invention, there is provided aheat-sensitive recording material in which a chromogenic dye-precursorcomprises:

(A) a mixture comprising at least two divinyl phthalide compoundsrepresented by the formula (I): ##STR5## wherein R¹ and R² representrespectively alkyl group of 1 to 6 carbon atoms, alkyl group of 1 to 4carbon atoms having an alkoxy group of 1 to 4 carbon atoms or cycloalkylgroup of 5 to 7 carbon atoms, X¹ and X² represent respectively hydrogenatom, alkyl group of 1 to 8 carbon atoms, alkoxy group of 1 to 8 carbonatoms, alkoxy group of 1 to 4 carbon atoms having an alkoxy group of 1to 4 carbon atoms, cycloalkoxy group of 5 to 7 carbon atoms, alkenyloxygroup of 3 to 8 carbon atoms, benzyloxy group, substituted benzyloxygroup, furfuryloxy group, tetrahydrofurfuryloxy group, phenyl group,substituted phenyl group, phenoxy group, substituted phenoxy group,fluorine atom, chlorine atom or bromine atom, m and n represent 0 orinteger of 1 to 4, m+n=4 and R¹ and R² may join together to form aheterocyclic ring, or

(B) a mixture of the divinyl phthalide compound(s) represented by theformula (I) and at least one compound selected from the compoundsrepresented by the formulas (II), (III) and (IV): ##STR6## wherein R³-R¹⁴ represent alkyl group of 1 to 6 carbon atoms, alkyl group of 1 to 4carbon atoms each having an alkoxy group of 1 to 4 carbon atoms,cycloalkyl group of 5 to 7 carbon atoms, phenyl group, substitutedphenyl group or tetrahydrofurfuryl group, p and q represent 0 or integerof 1 to 4, p+q=4, X³ represents hydrogen atom, alkyl group of 1 to 4carbon atoms or chlorine atom, X⁴ and X⁵ respectively represent hydrogenatom, alkyl group of 1 to 4 carbon atoms, fluorine atom, chlorine atomor trifluoromethyl group, R³ and R⁴, R⁵ and R⁶, R⁷ and R⁸, R⁹ and R¹⁰,R¹¹ and R¹², and R¹³ and R¹⁴ may join together to form heterocyclicrings.

DETAILED DESCRIPTION OF THE INVENTION

Divinyl phthalide compounds of the formula (I) are described in Japanesepatent application Nos. 61-87619, 61-88961 and 61-102909 (correspondingto U.S. patent applications No. (unknown) filed Apr. 13, 1987 and No.(unknown) filed Apr. 13, 1987), which are substantially colorless bythemselves, extremely stable in an atmospheric air, free fromsublimation and spontaneous color development (background fogging), andare highly soluble to an organic solvent. In addition, they are rapidlyconverted to black-colored substances by developer and form developedcolor image excellent in the light fastness. Further, since thedeveloped color images show intense absorption at 700-1000 nm inaddition to the visible region, they have an advantageous feature ofenabling reading by an optical character reader (OCR, OMR) and a barcode reader using near infrared rays.

Further, the compounds of the formula (II) are disclosed in EuropeanPatent No. 0124377A2 and the compounds of the formula (III) aredisclosed in U.S. Pat. No. 4,020,056 and No. 4,107,428. These compoundsare chromogenic dye-precursor and the developed color images formedtherefrom show an absorption in the near infrared region. The compoundsof the formula (IV) are disclosed in U.S. Pat. No. 3,669,711, No.3,681,390, No. 3,920,510, No. 3,925,457, No. 3,959,571 and No.4,444,591, and these compounds are fluoran compounds which may beconverted to green or black substances showing no absorption in the nearinfrared region, and have an effect of improving the storage stability,developed color tone, developed color density and light fastness of thedeveloped color image.

The heat-sensitive recording material can include, for example,heat-sensitive recording paper, electrically heated heat-sensitiverecording paper, transfer reaction type heat-sensitive recording paper,etc. using paper, synthetic paper or plastic film as the base.

Specific examples of the compounds of the formulas (I)-(IV) used in thepresent invention will be described below but the compound is no waylimited only thereto.

1. Compound represented by the formula (I):

    __________________________________________________________________________     ##STR7##                                        (I)                           No.poundCom-                                                                      ##STR8##  X.sup.1      X.sup.2     nm   bisphenol Acolor                 __________________________________________________________________________                                                byDeveloped                            ##STR9## H            H           m = 4 n = 0                                                                        reddish black                     2                                                                                  ##STR10##                                                                              H            p-CH.sub.3  m = 4 n = 0                                                                        reddish black                     3                                                                                  ##STR11##                                                                              H            p-OCH.sub.3 m = 4 n = 0                                                                        black                             4                                                                                  ##STR12##                                                                              m-OCH.sub.3  p-OCH.sub.3 m = 4 n = 0                                                                        black                             5                                                                                  ##STR13##                                                                              H            p-OCH.sub.3 m = 0 n = 4                                                                        black                             6                                                                                  ##STR14##                                                                              H            p-OCH.sub.3 m = 1 (5-Cl) n = 3                                                                 black                             7                                                                                  ##STR15##                                                                              H            p-OC.sub.2 H.sub.5                                                                        m = 4 n = 0                                                                        black                             8                                                                                  ##STR16##                                                                              H            p-OCH.sub.3 m = 4 n = 0                                                                        black                             9                                                                                  ##STR17##                                                                              H            p-OCH.sub.3 m = 4 n = 0                                                                        black                             10                                                                                 ##STR18##                                                                              p-CH.sub.3   H           m = 4 n = 0                                                                        reddish black                     11                                                                                 ##STR19##                                                                              H            p-OCH.sub.3 m = 4 n = 0                                                                        black                             12                                                                                 ##STR20##                                                                              H            p-OCH.sub.3 m = 4 n = 0                                                                        black                             13                                                                                 ##STR21##                                                                              H            p-OCH.sub.3 m = 4 n = 0                                                                        black                             14                                                                                 ##STR22##                                                                              H            p-CH.sub.3  m = 4 n = 0                                                                        reddish black                     15                                                                                 ##STR23##                                                                              H            p-OCH.sub.3 m = 4 n = 0                                                                        black                             16                                                                                 ##STR24##                                                                              H            p-OCH.sub.3 m = 4 n = 0                                                                        black                             17                                                                                 ##STR25##                                                                              H            p-OCH.sub.3 m = 4 n = 0                                                                        black                             18                                                                                 ##STR26##                                                                              H            p-OC.sub.3 H.sub.7                                                                        m = 4 n = 0                                                                        black                             19                                                                                 ##STR27##                                                                              H            p-Oiso-C.sub.4 H.sub.9                                                                    m = 4 n = 0                                                                        black                             20                                                                                 ##STR28##                                                                              H            p-OC.sub.5 H.sub.11                                                                       m = 4 n = 0                                                                        black                             21                                                                                 ##STR29##                                                                              H            p-OC.sub.2 H.sub.4 OCH.sub.3                                                              m = 4 n = 0                                                                        black                             22                                                                                 ##STR30##                                                                               ##STR31##   H           m = 4 n = 0                                                                        black                             23                                                                                 ##STR32##                                                                              H            p-OCH.sub.2 CHCH.sub.2                                                                    m = 4 n = 0                                                                        black                             24                                                                                 ##STR33##                                                                              H                                                                                           ##STR34##  m = 4 n = 0                                                                        black                             25                                                                                 ##STR35##                                                                              H            p-Oiso-C.sub.3 H.sub.7                                                                    m = 4 n = 0                                                                        black                             26                                                                                 ##STR36##                                                                              H            p-OC.sub.4 H.sub.9                                                                        m = 4 n = 0                                                                        black                             27                                                                                 ##STR37##                                                                              H            p-OCH.sub.2CHCH.sub.2                                                                     m = 4 n = 0                                                                        black                             28                                                                                 ##STR38##                                                                              H                                                                                           ##STR39##  m = 4 n = 0                                                                        black                             29                                                                                 ##STR40##                                                                               ##STR41##   H           m = 4 n = 0                                                                        black                             30                                                                                 ##STR42##                                                                               ##STR43##   H           m = 4 n = 0                                                                        reddish black                     31                                                                                 ##STR44##                                                                               ##STR45##   H           m = 4 n = 0                                                                        black                             32                                                                                 ##STR46##                                                                               ##STR47##   H           m = 4 n = 0                                                                        black                             33                                                                                 ##STR48##                                                                               ##STR49##   H           m = 4 n = 0                                                                        black                             __________________________________________________________________________

2. Compound represented by the formula (II):

    __________________________________________________________________________     ##STR50##                        (II)                                         No.Compound                                                                         ##STR51##                                                                              ##STR52##                                                                            ##STR53##                                                                            by bisphenol ADeveloped color                   __________________________________________________________________________    34                                                                                   ##STR54##                                                                              ##STR55##                                                                            ##STR56##                                                                           greenish blue                                    35                                                                                   ##STR57##                                                                              ##STR58##                                                                            ##STR59##                                                                           greenish blue                                    36                                                                                   ##STR60##                                                                              ##STR61##                                                                            ##STR62##                                                                           greenish blue                                    37                                                                                   ##STR63##                                                                              ##STR64##                                                                            ##STR65##                                                                           greenish blue                                    38                                                                                   ##STR66##                                                                              ##STR67##                                                                            ##STR68##                                                                           greenish blue                                    39                                                                                   ##STR69##                                                                              ##STR70##                                                                            ##STR71##                                                                           greenish blue                                    40                                                                                   ##STR72##                                                                              ##STR73##                                                                            ##STR74##                                                                           greenish blue                                    41                                                                                   ##STR75##                                                                              ##STR76##                                                                            ##STR77##                                                                           greenish blue                                    42                                                                                   ##STR78##                                                                              ##STR79##                                                                            ##STR80##                                                                           greenish blue                                    __________________________________________________________________________

3. Compound represented by the formula (III):

    __________________________________________________________________________     ##STR81##                              (III)                                  No.Compound                                                                          ##STR82##                                                                                ##STR83##  qp    bisphenol Acolor byDeveloped              __________________________________________________________________________    43                                                                                    ##STR84##                                                                                ##STR85## p = 4 q = 0                                                                         green                                      44     "          "          p = 0 "                                                                       q = 4                                            45     "          "          p = 1 "                                                                       (5-Cl)                                                                        q = 3                                            46     "          "          p = 2 "                                                                       (5.6-Cl.sub.2)                                                                q = 2                                            47                                                                                    ##STR86##                                                                                ##STR87## p = 4 q = 0                                                                         "                                          48                                                                                    ##STR88##                                                                                ##STR89## p = 4 q = 0                                                                         "                                          49                                                                                    ##STR90##                                                                                ##STR91## p = 4 q = 0                                                                         "                                          50                                                                                    ##STR92##                                                                                ##STR93## p = 4 q = 0                                                                         "                                          51     "                                                                                         ##STR94## p = 4 q = 0                                                                         "                                          52     "          "          p = 0 "                                                                       q = 4                                            53                                                                                    ##STR95##                                                                                ##STR96## p = 4 q = 0                                                                         "                                          54                                                                                    ##STR97## "          p = 4 q = 0                                                                         "                                          __________________________________________________________________________

4. Compound represented by the formula (IV):

    __________________________________________________________________________     ##STR98##                         (IV)                                        No.Compound                                                                         ##STR99##    X.sup.3                                                                          X.sup.4                                                                           X.sup.5                                                                           bisphenol Acolor byDeveloped                   __________________________________________________________________________    55                                                                                   ##STR100##  H  H   H   greenish black                                  56    "            "  "   p-CH.sub.3                                                                        "                                               57                                                                                   ##STR101##  "  "   H   "                                               58                                                                                   ##STR102##  "  "   "   "                                               59                                                                                   ##STR103##  "  "   "   "                                               60                                                                                   ##STR104##  CH.sub.3                                                                         "   "   black                                           61    "            H  o-Cl                                                                              "   "                                               62    "            "  H   m-CF.sub.3                                                                        greenish black                                  63    "            Cl "   H   "                                               64                                                                                   ##STR105##  CH.sub.3                                                                         "   "   black                                           65                                                                                   ##STR106##  CH.sub.3                                                                         H   H   black                                           66                                                                                   ##STR107##  "  "   "   "                                               67                                                                                   ##STR108##  "  "   "   "                                               68    "            H  "   o-Cl                                                                              "                                               69                                                                                   ##STR109##  CH.sub.3                                                                         o-CH.sub.3                                                                        m-CH.sub.3                                                                        "                                               70                                                                                   ##STR110##  "  H   H   "                                               71                                                                                   ##STR111##  "  "   "   "                                               72                                                                                   ##STR112##  "  "   "   "                                               73                                                                                   ##STR113##  "  "   "   "                                               74                                                                                   ##STR114##  "  "   "   "                                               75                                                                                   ##STR115##  "  "   "   "                                               76                                                                                   ##STR116##  "  "   "   "                                               77                                                                                   ##STR117##  H  o-F H   greenish black                                  78                                                                                   ##STR118##  "  "   "   "                                               79                                                                                   ##STR119##  "  o-Cl                                                                              "   black                                           80                                                                                   ##STR120##  "  "   "   "                                               81                                                                                   ##STR121##  CH.sub.3                                                                         H   H   "                                               82                                                                                   ##STR122##  "  "   "   "                                               83                                                                                   ##STR123##  "  "   "   "                                               84                                                                                   ##STR124##  "  "   "   "                                               __________________________________________________________________________

The chromogenic dye-precursor according to the present invention is amixture comprising at least two compounds represented by the formula (I)or a mixture of a compound represented by the formula (I) and at leastone compound selected from the compounds represented by the formulas(II)-(IV). Also, a mixture of at least two compounds represented by theformula (I) in which R¹ is methyl or ethyl group, R² is methyl, ethyl,isobutyl, methoxyethyl or cyclohexyl group, or R¹ and R² may jointogether to form ##STR125## X¹ represents hydrogen atom, methyl ormethoxy group, X² represents hydrogen atom, methyl, methoxy, ethoxypropoxy, isopropoxy, butoxy, isobutoxy or benzyloxy group, m is 0, 1 or4 and n is 0, 3 or 4, m+n=4, and a mixture of the compound representedby the formula (I) in which R¹, R², X¹, X², m and n is the same asdefined just above with at least one compound selected from the groupconsisting of a compound represented by the formula (II) in which R³ ismethyl or ethyl group, R⁴ is methyl, ethyl, methoxyethyl or cyclohexylgroup, or R³ or R⁴ may join together to form ##STR126## R⁵ and R⁶ areindependently methyl or ethyl group, R⁷ and R⁸ are independently methyl,ethyl, propyl group or R⁷ and R⁸ may join together to form ##STR127## acompound represented by the formula (III) in which R⁹ is methyl, ethylor methoxyethyl group, R¹⁰ is methyl, ethyl or cyclohexyl group, R⁹ andR¹⁰ may join together to form ##STR128## R¹¹ is methyl, ethyl ormethoxyethyl group, R¹² is methyl or ethyl group, R¹¹ and R¹² may jointogether to form ##STR129## p is 0, 1, 2 or 4, q is 0, 2, 3 or 4 andp+q=4, and a compound represented by the formula (IV) in which R¹³ ismethyl, ethyl or butyl group, R¹⁴ is ethyl, propyl, butyl, i-pentyl,hexyl, ethoxypropyl, cyclohexyl, methylphenyl group or ##STR130## or R¹³and R¹⁴ may join together to form ##STR131## X³ is hydrogen atom,chlorine atom or a methyl group, X⁴ is hydrogen atom, chlorine atom ormethyl group, and X⁵ is hydrogen atom, chlorine atom, methyl ortrifluoromethyl group, are preferred. Further, a mixture of at least twoof the compounds No. 1 to No. 33 (compounds of the formula (I)), or amixture of a compound selected from the compounds No. 1 to No. 33 withat least one selected from the group consisting of the compounds No. 34to No. 42 (compounds of the formula (II)), the compounds No. 43 to No.54 (compounds of the formula (III)) and the compounds No. 55 to No. 84(compounds of the formula (IV)) are more preferred.

Furthermore, a mixture of at least two compounds of the formula (I) inwhich R¹ is methyl or ethyl group, R² is methyl or ethyl group, R¹ andR² may join together to form ##STR132## X¹ is hydrogen atom, methyl ormethoxy group, X² is a hydrogen atom, methoxy or ethoxy group, m=4 andn=0, and a mixture of the compound(s) of the formula (I) listed abovewith at least one selected from the group consisting of the compound ofthe formula (II) in which R³ is methyl or ethyl group, R⁴ is methyl orethyl group, R⁵ is methyl or ethyl group, R⁶ is methyl or ethyl group,R⁷ is methyl, ethyl or propyl group, R⁸ is methyl, ethyl or propylgroup, the compound of the formula (III) in which R⁹ is methyl or ethylgroup, R¹⁰ is methyl or ethyl group, R⁹ and R¹⁰ may join together toform ##STR133## R¹¹ is methyl or ethyl group, R¹² is methyl or ethylgroup, R¹¹ and R¹² may join together to form ##STR134## p is 0 or 4, qis 0 or 4 and p+q=4 and the compound of the formula (IV) in which R¹³ isa methyl, ethyl, propyl or butyl group, R¹⁴ is ethyl, butyl, i-pentyl,hexyl, ethoxypropyl, cyclohexyl, methylphenyl or ##STR135## R¹³ and R¹⁴may join together to form ##STR136## , X³ is hydrogen atom or methylgroup, X⁴ is hydrogen atom, chlorine atom or methyl group and X⁵ ishydrogen atom or methyl group are most preferred.

The content of the compound of the formula (I) in the mixture of thecompound(s) of the formula (I) and at least one selected from thecompounds of the formulas (II)-(IV) is not less than 10% by weight,preferably, not less than 20% by weight and, particularly preferably,not less than 30% by weight.

The compound of the formula (I) used in the present invention can beobtained by condensating 2 mol of the ethylene derivative of thefollowing formula (V) and 1 mol of the phthalic acid derivative of thefollowing formula (VI) under the presence of a dehydrating agent such asacetic anhydride and sulfuric acid at a temperature from 80° to 150° C.##STR137## wherein R¹ and R² represent respectively alkyl group of 1 to6 carbon atoms, alkyl group of 1 to 4 carbon atoms having an alkoxygroup of 1 to 4 carbon atoms or cycloalkyl group of 5 to 7 carbon atoms,X¹ and X² represent respectively hydrogen atom, alkyl group of 1 to 8carbon atoms, alkoxy group of 1 to 8 carbon atoms, alkoxy group of 1 to4 carbon atoms having an alkoxy group of 1 to 4 carbon atoms,cycloalkoxy group of 5 to 7 carbon atoms, alkenyloxy group of 3 to 8carbon atoms, benzyloxy group, substituted benzyloxy group, furfuryloxygroup, tetrahydrofurfuryloxy group, phenyl group, substituted phenylgroup, phenoxy group, substituted phenoxy group, fluorine atom, chlorineatom or bromine atom, m and n represent 0 or integer of 1 to 4, m+n=4,and R¹ and R² may joint together to form a heterocyclic ring.

The ethylene derivative of the formula (V) described above can besynthesized by any one of the following Grignard reactions a, b, c:##STR138## (where R¹, R², X¹, X² have the same meanings as defined aboveand X is halogen atom).

For preparing the heat-sensitive recording material by using thechromogenic dye-precursor according to the present invention, knownmethods described, for example, in Japanese patent publication No.45-14039 (1970) (corresponding to U.S. Pat. No. 3,539,375), Japanesepatent laying-open (KOKAI) No. 59-33186 (1984), etc. can be adopted.Further, the chromogenic dye-precursor may be mixed by previouslydissolving or melting them, or mixing crystals thereof before or afterthe pulverization.

Further, other chromogenic dye-prescursor which can assume variouscolors other than those of the substance derived from the compound ofthe formulas (I)-(IV) may be mixed in order to attain more completecolor hue, coloring sensitivity, coloring density, etc.

For instance,

3,3-bis(aminophenyl)-6-aminophthalide,

3,3-bis(indolyl)phthalide, 3-aminofluoran, aminobenzofluoran,

spiropyran, phenoxazine, leuco auramine, carbazolylmethane,

3-indolyl-3-(amino)phenylphthalide and

3-indolyl-3-(aminophenyl)azaphthalide can be used.

As a binder for preparing the heat-sensitive recording material,polyvinyl alcohol, methylcellulose, hydroxy ethylcellulose,carboxymethylcellulose, gum arabic, gelatin, starch, polyvinylpyrrolidone, styrene-maleic anhydride copolymer and the like can beused. As the developer, clay, bentonite, active white clay, zincchloride, zinc salt of salicylic acid derivative, p-phenylphenolformalin resin, p-octylphenyl formalin resin and zinc salt thereof,methyl 4-hydroxybenzoate, benzyl 4-hydroxybenzoate, bisphenol A,4,4'-thiodiphenol,

bis-(4-hydroxy-3-methylphenyl)sulfide,

4,4'-dihydroxydiphenyl sulfone,

4-hydroxy-4'-methyldiphenyl sulfone,

4-hydroxy-4'-propoxydiphenyl sulfone,

4,4'-dihydroxy-3,3'-diallyldiphenyl sulfone,

1,5-di(4-hydroxyphenylthio)-3-oxapentane,

1,7-di(4-hydroxyphenylthio)-3,5-dioxaheptane,

1,8-di(4-hydroxyphenylthio)-3,6-dioxaoctane,

bis(4-hydroxy-3-methylphenyl)sulfide,

dimethyl hydroxyphthalate and

2,4-dihydroxybenzophenone can be used.

As the sensitizer, urea, phthalic anhydride, acetanilide, paraffin wax,carnauba wax, higher fatty acid, higher fatty acid ester, higher fattyacid amide, phthalic acid ester, terephthalic acid ester, benzyl4-benzyloxybenzoate, naphthol benzyl ether, 1,4-dialkoxynaphthalene,m-terpheyl,

p-benzylbiphenyl, dibenzylbenzene,

1-hydroxy-2-naphthoic acid ester,

2-hydroxy-3-naphthoic acid ester,

4,4'-dialkoxydiphenyl sulfone, benzamide, diphenylamine,benzenesulfonamide, benzenesulfonanilide, carbazole and hydroquinonebenzyl ether can be mixed therewith.

Further, addition of various antioxidants, anti-aging agents and UVabsorbers, or overcoat with polymeric material for the heat-sensitiverecording material is effective for the improvement in the lightfastness and the storage stability of the colored images.

The heat-sensitive recording material according to the present inventioncan provide the black colored images having been increasingly demanded,which shows absorption at near infrared region as well as excellentperformances in moisture resistance, resistance to plasticizer, oilresistance, light fastness and the like and, accordingly, it is of highindustrial value as heat-sensitive recording paper for OCR or the like.

This invention will now be described more specifically referring to thefollowing non-limitative examples.

EXAMPLE 1

    ______________________________________                                        (1) Preparation of Chromogenic Dye-precursor Dispersion                       (Liquid A)                                                                    ______________________________________                                        3,3-bis[2-(p-dimethylaminophenyl)-2-                                                                   3 parts                                              (p-methoxyphenyl)ethenyl]-4,5,6,7-tetra                                       chlorophthalide (Compound No. 3)                                              3,3-bis[2-(p-pyrrolidinophenyl)-2-                                                                     3 parts                                              (p-methoxyphenyl)ethenyl]-4,5,6,7-tetra                                       chlorophthalide (Compound No. 11)                                             Kaolin                  15 parts                                              Aqueous 10% polyvinyl alcohol solution                                                                100 parts                                             Water                   85 parts                                              ______________________________________                                    

The mixture was pulverized by using a paint shaker (manufactured by ToyoSeiki Co.) till the average particle diameter of the chromogenicdye-precursor was to 2 μm.

    ______________________________________                                        (2) Preparation of Developer Dispersion (Liquid B)                            ______________________________________                                        Bisphenol A             15 parts                                              Zinc stearate           10 parts                                              Aqueous 10% polyvinyl alcohol solution                                                                100 parts                                             ______________________________________                                    

The mixture was pulverized by a paint shaper till the average particlediameter was to 3 μm.

(3) Preparation and Coating of Heat Sensitive Coating Liquid

10 parts of the liquid A and 6.5 parts of the liquid B were mixed andstirred to obtain a heat-sensitive coating liquid. The coating liquidwas uniformly coated on a paper sheet so as to obtain a paper having a 6g/m² of the coated material in dry weight by using a wire bar, followedby drying to obtain heat-sensitive recording paper. The heat-sensitiverecording paper was colorless, free from background fogging and coloreddensely black rapidly by heating with a thermopen or the like. Thedeveloped color image was excellent in the light fastness and themoisture resistance and since it had an intense absorption in 700-1000nm, OCR reading was possible. Further, the coated surface was alsoexcellent in the light fastness and not pigmented under sunlightirradiation.

EXAMPLES 2-21

Heat-sensitive recording paper sheets were obtained by the sameprocedures as in Example 1 except mixing the chromogenic dye-precursorsshown in Table 1 instead of 3 parts of the compound No. 3 and thecompound No. 11.

These heat-sensitive recording paper sheets had excellent performancelike that in Example 1.

COMPARATIVE EXAMPLE 1

Heat-sensitive recording paper sheet was obtained in the same proceduresas in Example 1 except using 6 parts of the No. 3 compound as thechromogenic dye-precursor.

COMPARATIVE EXAMPLES 2-13

Heat-sensitive recording paper sheets were obtained by the sameprocedures as in Example 1 except using the compounds shown in Table 2as the chromogenic dye-precursor.

(TEST)

The moisture resistance and the resistance to plasticizer were tested bythe following methods for the heat-sensitive recording paper sheetsobtained in the Examples and the Comparative Examples. The results areshown in Table 1 and Table 2.

(1) Moisture Resistance Test

Respective heat-sensitive paper sheets were evenly colored by using aheat-sensitive coloring tester (manufactured by Matsushita Denshi BuhinCo.) with an application voltage at 15 volt and a pulse width of 2.5 msec. After leaving the colored images for 4 days in an atmosphere at atemperature of 40° C. and a relative humidity of 90%, the lightabsorption at 900 nm was measured by using a spectrophotometer (Model UV365, manufactured by Shimazu Seisakusho, Co.). Then, the image residualrate was determined by the following equation to define it as themoisture resistance: ##EQU1##

The specimens of Comparative Example 8, 9, 10 composed only of thecompound of the general formula (IV) were measured at 600 nm (laso inthe plasticizer-resistance test).

(2) Plastizer-resistance test

The image area colored under the same conditions as on (1) above wascovered with a soft vinyl chloride sheet (Kuke-64, manufactured byKokuyo Co.) and placed in a thermostat at 60° C. for 3 hours under theload of 4 g/cm². The light absorption at 900 nm was measured in the samemanner as in (1) and the image residual ratio was determined by thefollowing equation to define it as the plasticizer-resistance: ##EQU2##

                  TABLE 1                                                         ______________________________________                                             Amount of chromogenic           Plasti-                                  Ex-  dye-precursor mixed             cizer                                    am-  Compound of  Compound of the                                                                            Moisture                                                                              resis-                                 ple  the general  general formula                                                                            Resistance                                                                            tance                                  No.  formula (I)  (II), (III), (IV)                                                                          (%)     (%)                                    ______________________________________                                         1   No. 3 (3 parts)           68      89                                          No. 11 (3 parts)                                                          2   No. 3 (4 parts)           59      88                                          No. 11 (2 parts)                                                          3   No. 3 (2 parts)           73      88                                          No. 11 (4 parts)                                                          4   No. 3 (3 parts)           60      79                                          No. 15 (3 parts)                                                          5   No. 11 (3 parts)                                                                           No.34 (3 part)                                                                             86      88                                      6   No. 3 (3 parts)                                                                            No.34 (3 part)                                                                             80      81                                      7   No. 3 (3 parts)                                                                            No.43 (3 part)                                                                             85      98                                      8   No. 3 (3 parts)                                                                            No.61 (3 part)                                                                             70      85                                      9   No. 3 (3 parts)                                                                            No.71 (3 part)                                                                             82      86                                     10   No. 3 (3 parts)                                                                            No.59 (3 part)                                                                             73      91                                     11   No. 3 (3 parts)                                                                            No.65 (3 part)                                                                             82      86                                     12   No. 3 (4 parts)                                                                            No.65 (2 part)                                                                             80      83                                     13   No. 3 (3 parts)                                                                            No.60 (3 part)                                                                             84      86                                     14   No. 3 (4 parts)                                                                            No.60 (2 part)                                                                             81      82                                     15   No. 3 (4.5 parts)                                                                          No.60 (1.5 part)                                                                           75      78                                     16   No. 3 (2 parts)           70      80                                          No. 10 (2 parts)                                                              No. 11 (2 parts)                                                         17   No. 3 (2 parts)                                                                            No.43 (2 part)                                                                             90      95                                          No. 11 (2 parts)                                                         18   No. 3 (2 parts)                                                                            No.65 (2 part)                                                                             76      96                                          No. 11 (2 parts)                                                         19   No. 3 (2 parts)                                                                            No.34 (2 part)                                                                             85      85                                                       No.60 (2 part)                                              20   No. 3 (2 parts)                                                                            No.34 (2 part)                                                                             87      88                                                       No.43 (2 part)                                              21   No. 3 (2 parts)                                                                            No.60 (1 part)                                                                             86      87                                          No. 11 (2 parts)                                                                           No.65 (1 part)                                              ______________________________________                                    

                  TABLE 2                                                         ______________________________________                                                                Moisture Plasticizer-                                 Comparative                                                                              Chromogenic  resistance                                                                             resistance                                   Example No.                                                                              dye-precursor                                                                              (%)      (%)                                          ______________________________________                                        1          No. 3 (6 parts)                                                                            33       70                                           2          No. 10 (6 parts)                                                                           63       70                                           3          No. 11 (6 parts)                                                                           80       83                                           4          No. 15 (6 parts)                                                                           63       84                                           5          No. 34 (6 parts)                                                                           81       92                                           6          No. 36 (6 parts)                                                                           71       84                                           7          No. 43 (6 parts)                                                                           89       98                                           8          No. 59 (6 parts)                                                                           86       95                                           9          No. 60 (6 parts)                                                                           94       91                                           10         No. 65 (6 parts)                                                                           93       92                                           11         No. 43 (3 parts)                                                                           86       95                                                      No. 34 (3 parts)                                                   12         No. 34 (3 parts)                                                                           77       88                                                      No. 36 (3 parts)                                                   13         No. 34 (3 parts)                                                                           59       62                                                      No. 65 (3 parts)                                                   ______________________________________                                    

From the test, it was confirmed that the heat-sensitive recording paperaccording to the present invention is excellent in the moistureresistance and the resistance to plasticizer.

What is claimed is:
 1. A heat-sensitive recording material comprising asubstrate on which there is applied:(1) an effective amount of:(i) achromogenic dye-precursor selected from the group consisting of amixture of at least two divinyl phthalide compounds represented by theformula (I); (ii) a mixture of a divinyl phthalide compound representedby the formula (I) and a compound represented by the formula (II); (iii)a mixture of a divinyl phthalide compound represented by the formula (I)and a compound represented by the formula (III); (iv) a mixture ofadivinyl phthalide compound represented by the formula (I) a compoundrepresented by the formula (IV); (v) a mixture of a divinyl phthalidecompound represented by the formula (I), a compound represented by theformula (II) and a compound represented by the formula (III); (vi) amixture of a divinyl phthalide compound represented by the formula (I),a compound represented by the formula (II) and a compound represented bythe formula (IV); and (vii) a mixture of a divinyl phthalide compoundrepresented by the formula (I) and at least two compounds represented bythe formula (IV); wherein said divinyl phthalide compounds representedby the formula (I) are as follows: ##STR139## wherein, R¹ and R²represent respectively an alkyl group of 1 to 6 carbon atoms, an alkylgroup of 1 to 4 carbon atoms having an alkoxy group of 1 to 4 carbonatoms or a cycloalkyl group of 5 to 7 carbon atoms; X¹ and X² representrespectively a hydrogen atom, an alkyl group of 1 to 8 carbon atoms, analkoxy group of 1 to 8 carbon atoms, an alkoxy-alkoxy group wherein eachalkoxy subgroup is of 1 to 4 carbon atoms, a cycloalkoxy group of 5 to 7carbon atoms, an alkenyloxy group of 3 to 8 carbon atoms, a benzyloxygroup, a substituted benzyloxy group, a furfuryloxy group, atetrahydrofurfuryloxy group, a phenyl group, a substituted phenyl group,a phenoxy group, a substituted phenoxy group, a fluorine atom, achlorine atom or bromine atom; m and n represent 0 or an integer of 1 to4; m+n=4, and R¹ and R² may join together to form a heterocyclic ring,and wherein each of said compounds represented by the formulas (II),(III) and (IV) are as follows: ##STR140## where, R³ -R¹⁴ represent analkyl group of 1 to 6 carbon atoms, an alkyl group of 1 to 4 carbonatoms each having an alkoxy group of 1 to 4 carbon atoms, a cycloalkylgroup of 5 to 7 carbon atoms, a phenyl group, a substituted phenyl groupor tetrahydrofurfuryl group; p and q represent 0 or an integer of 1 to4; p+q=4; X³ represents a hydrogen atom, an alkyl group of 1 to 4 carbonatoms or a chlorine atom; X⁴ and X⁵ respectively represent a hydrogenatom, a chlorine atom or trifluromethyl group; and wherein R³ and R⁴,R⁶, R⁷ and R⁸, R⁹ and R¹⁰, R¹¹ and R¹², and R¹³ and R¹⁴ may jointogether to form heterocyclic rings, and wherein said heat-sensitiverecording material further comprises (2) a developer, and (3) a binder.2. A heat-sensitive recording material as defined in claim 1, whereinsaid chromogenic dye-precursor is a mixture selected from mixtures of(a) a compound of said formula (I) and a compound of said formula (IV),(b) a compound of said formula (I), a compound of said formula (II) anda compound of said formula (IV), and (c) a compound of said formula (I)and two different compounds of said formula (IV).
 3. A heat-sensitiverecording material as defined in claim 1, wherein said chromogenicdye-precursor is a mixture selected from mixtures of (a) a compound ofsaid formula (I) and a compound of said formula (IV), and (b) a compoundof said formula (I) and two different compounds of said formula (IV). 4.A heat-sensitive recording material as defined in claim 1, wherein thedivinyl phthalide compound is a compound in which R¹ represents methylor ethyl group, R² represents methyl, ethyl, isobutyl, methoxyethyl orcyclohexyl group, or R¹ and R² may join together to form ##STR141## X¹represents hydrogen atom, methyl or methoxy group, X² representshydrogen atom, methyl, methoxy or ethoxy group, m is 0, 1 or 4, n is 0,3 or 4, and m+n=4 in the formula (I),the compound represented by theformula (II) is one in which R³ represents methyl or ethyl group, R⁴methyl, ethyl, methoxyethyl or cyclohexyl group or R³ and R⁴ may jointogether to form ##STR142## R⁵ and R⁶ represent independently methyl orethyl group, R⁷ and R⁸ represent independently methyl, ethyl or propylgroup or R⁷ and R⁸ may join together to form ##STR143## in the formula(II), the compound represented by the formula (III) is one in which R⁹represents methyl, ethyl or methoxyethyl group, R¹⁰ represents methyl,ethyl or cyclohexyl group, R⁹ and R¹⁰ may join together to form##STR144## R¹¹ represents methyl, ethyl or methoxyethyl group, R¹²represents methyl or ethyl, R¹¹ and R¹² may join together to form##STR145## p is 0, 1, 2 or 4, q is 0, 2, 3 or 4, p+q=4 in the formula(III), and the compound represented by the formula (IV) is one in whichR¹³ represents methyl, ethyl or butyl group, R¹⁴ represents ethyl,propyl, butyl, i-pentyl, hexyl, ethoxypropyl, cyclohexyl, methylphenylor ##STR146## or R¹³ and R¹⁴ may join together to form ##STR147## X³represents hydrogen atom, chlorine atom or methyl group, X⁴ representshydrogen atom, chlorine atom or methyl group and X⁵ represents hydrogenatom, chlorine, methyl group and trifluoromethyl group in the formula(IV).
 5. A heat-sensitive recording material as defined in claim 4,wherein the divinyl phthalide compound is a compound in which R¹represents methyl or ethyl group, R² represents methyl or ethyl group,or R¹ and R² may join together to form ##STR148## X¹ represents hydrogenatom, methyl or methoxy group, X² represents hydrogen atom, methoxy orethoxy group, m=4 and n=0 in the formula (I),the compound represented bythe formula (II) is one in which R³ represents methyl or ethyl group, R⁴represents methyl or ethyl group, R⁵ represents methyl or ethyl group,R⁶ represents methyl or ethyl group, R⁷ represents methyl, ethyl orpropyl group, R⁸ represents methyl, ethyl or propyl group in the formula(II), the compound represented by the formula (III) is one in which R⁹represents methyl or ethyl group, R¹⁰ represents methyl or ethyl group,R⁹ and R¹⁰ may join together to form ##STR149## R¹¹ represents methyl orethyl group, R¹² represents methyl or ethyl group, R¹¹ and R¹² may jointogether to form ##STR150## p is 0 or 4, q is 0 or 4 and p+q=4 in theformula (III), and the compound represented by the formula (IV) is onein which R¹³ represents methyl, ethyl or butyl group, R¹⁴ representsethyl, propyl, butyl, i-pentyl, hexyl, ethoxypropyl, cyclohexyl,methylphenyl group or ##STR151## R¹³ and R¹⁴ may join together to form##STR152## X³ represents hydrogen atom or methyl group, X⁴ representshydrogen atom, chlorine atom or methyl group and X⁵ represents hydrogenatom or methyl group in the formula (IV).
 6. A heat-sensitive recordingmaterial as defined in claim 1, wherein the content of the compoundrepresented by the formula (I) in the chromogenic dye-precursor mixtureis not less than 20% by weight.
 7. A heat-sensitive recording materialas defined in claim 6, wherein the content of the compound representedby the formula (I) in the chromogenic dye-precursor mixture is not lessthan 30% by weight.